This invention relates to variable optical attenuators employed in fiber-optic transmission systems, more particularly to small-size variable optical attenuators suitable for miniaturized fiber optic assemblies.
Optical attenuators are staple components in fiber optic transmission systems, and numerous designs of variable optical attenuators are known in the art. E. g. Colbourne et al. in U.S. Pat. No. 5,915,063 describe a variable optical attenuator with a flat mirror positioned opposite a pair of waveguides and with an actuator causing a controlled tilting of the mirror.
Robinson, in U.S. Pat. No. 6,137,941, discloses a microelectromechanical (MEMS) structure with a pivotable reflector facing a pair of waveguides and a lens between the waveguides and the reflector.
Thermal arched beam (TAB) actuators have recently been developed and are described e.g. in U.S. Pat. Nos. 5,909,078 (Wood et al.) and 5,994,816 (Dhuler et al.) as well as in a copending U.S. patent application Ser. No. 09/537,588 filed Mar. 28, 2000. The three specifications are hereby incorporated herein by reference.
In keeping with the ubiquitous trend towards miniaturization of fiber-optic assemblies and components, there is still a need for a compact, simple and fast-acting device for attenuating optical signals.
It has been recognized that in most attenuators and similar components using flat, uniform mirrors or reflectors, the coupling efficiency of the optical beam reflected from the mirror is a function of the degree of overlap of the reflected beam with the output port or waveguide, while the intensity of the reflected beam remains substantially unchanged over a range of positions of the mirror.
The present invention proposes a different approach, wherein the coupling efficiency of the attenuator is a function of reflectivity of the mirror/reflector.
In accordance with the invention, there is provided an optical attenuator comprising a substantially planar substrate, an input port for providing an input optical beam, a variable reflectivity mirror disposed substantially in the plane of the substrate and oriented to receive the input optical beam and provide a reflected optical beam, and an actuator for changing the position of the mirror to vary the strength of the reflected optical signal. The reflectivity of the mirror may vary as a function of a place on the mirror, or as a function of the position of the mirror relative to the input port and/or the output port, or both. The mirror may for example have varying reflectivity across its surface.